feat: Add Eurostar cancellation and rebooking policy

[MoritzWeber0]

• Remove the Friday / Saturday / Sunday rule as tickets are also available with departure times between 17:30 and 19:30
• Remove the personal tip highlight around HOTNAT and CIV as these are official rules and not a personal tip and I also found it harder to read it in the highlight boxes
• Add rebooking & cancellation policy

[github-actions]

Hi there! 👋

Thank you for your contribution to the FIP Guide! 🚀
We appreciate your effort in making rail staff travel information more accessible. 🚄

Checklist before merging:

• Added a description to the Pull Request
• Checked the License of new pictures (non-commercial use without attribution)
• Modified content in English
• Modified content in German
• Modified content in French

[netlify]

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